The present invention relates to a method for reducing mechanical stress on at least one component of the drive train of a motor vehicle having at least two wheels, of which at least one wheel is a drive wheel, wherein the motor vehicle has an anti-lock braking system and at least one electric machine which for driving precisely one drive wheel the motor vehicle is coupled to this drive wheel, and wherein a respective friction brake is associated at least two wheels of the motor vehicle. The present invention further relates to a motor vehicle with at least two wheels, of which at least one is a drive wheel, including a first friction brake associated with the first wheel and a second friction brake associated with the second wheel, and an anti-lock braking system which is configured to act individually on the friction brakes for each of the wheels of the motor vehicle.
Conventional friction brakes are commonly used as an actuator for an anti-lock braking system (ABS). Here, the ABS is able to generate, in addition to the braking torque requirements for the friction brake, also a torque request for the drive unit, for example the internal combustion engine. This interface to the drive unit is often referenced with the term engine braking control (CEB). The CEB is designed to selectively reduce the drag torque of the drive unit, which acts on the vehicle as an additional braking torque. In some situations, the ABS may even request from the drive unit a driving torque during a braking operation in order to, for example, quickly reduce the brake slip of the tire. The CEB may, of course, only affect the axles connected to the drive unit, i.e. the driven axles. In addition, the CEB may only affect all the wheels connected to the drive unit simultaneously. The effectiveness of the CEB is strongly dependent on the dynamics and control accuracy of the drive unit. In internal combustion engines, both the dynamics and the control accuracy are severely limited by the properties of thermodynamic processes.
For vehicles with electric drive on one or more axles, the ABS usually a similar or identical structure as for conventionally driven vehicles, i.e. vehicles propelled by an internal combustion engine. With electrical drive machines, an actuator is available to the CEB, which is significantly superior to the internal combustion engine with respect to dynamics and control accuracy.
In this context, DE 10 2005 033 354 A1 should be mentioned which, however, applies only to vehicles with a drive topology wherein an electric machine operates on two wheels. This requires a differential between the two drive wheels. The control method proposed in this document is based on the average of the two wheel rotation speeds. This document addresses in particular the damping of the vibrations in the part of the drive train located between the differential and the one electric machine.
DE 102 23 990 B4 discloses a method which relates to the allocation of the total braking torque to a regenerative brake and a friction brake. In particular, a method is described herein addresses the special situation of an imminent or active ABS control to be carried out exclusively with the friction brake. For this special situation, methods are described how an upcoming ABS control can be detected and how the torque of the regenerative brake can be reduced, wherein at the same time the torque of the friction brake is increased accordingly so as to eliminate unwanted changes in the vehicle deceleration.
Significantly more damage was clearly detected in the drive train of conventional motor vehicles where an electric machine is provided for driving exactly one drive wheel and is correspondingly coupled to this drive wheel, than in motor vehicles using a conventional internal combustion engine. The damaged components therefore must be designed with greater dimensions, resulting in an undesirable increase in cost.